Exploring the Bias: How Skin Colour Influences Oxygen Saturation Readings via Monte Carlo Simulations

Swamy, Suvvi; Liu, Chong; Correia, Ricardo; Hayes-Gill, Barrie; Morgan, Steve

Abstract

Significance: Understanding the root cause of reported oxygen saturation (SpO2) overestimation in heavily pigmented skin types to devise solutions toward enabling equity in pulse oximeter design.

Aim: To gain theoretical insights into the effect of skin tone on SpO2-R curves by using a three-dimensional, four-layer tissue model representing a finger.

Approach: A finger tissue model, comprising the epidermis, dermis, two arteries, and a bone, was developed using a Monte Carlo-based approach in the MCmatlab software. Two skin tones — light and dark were simulated by adjusting the absorption and scattering properties within the epidermal layer. Following this, SpO2-R curves were generated in various tissue configurations, including transmission and reflection mode using red and infrared wavelengths. Additionally, the influence of source-detector (SD) separation distances on both light and dark skin tissue models was studied.

Results: In transmission mode, SpO2-R curves did not deviate with change in skin tones because both pulsatile (AC) and non-pulsatile (DC) terms experienced equal attenuation at red and infrared wavelengths. However, in reflection mode, measurable variations in SpO2-R curves were evident. This was due to differential attenuation of the red components, that resulted in lower perfusion index at the red wavelength in darker skin. As the SD separation increased, the effect of skin tone on SpO2-R curves in reflection mode became less pronounced, with largest SD separation exhibiting effects similar to those observed in transmission mode.

Conclusions: Monte Carlo simulations have demonstrated that different light pathlengths within the tissue contribute to overestimation of SpO2 in people with darker skin in reflection mode pulse oximetry. Increasing the SD separation may mitigate the effect of skin tone on SpO2 readings. These trends were not observed in transmission mode, however, further planned research using more complex models of the tissue is essential.

Citation

Swamy, S., Liu, C., Correia, R., Hayes-Gill, B., & Morgan, S. (2024). Exploring the Bias: How Skin Colour Influences Oxygen Saturation Readings via Monte Carlo Simulations. Journal of Biomedical Optics, 29(S3), Article S33308. https://doi.org/10.1117/1.JBO.29.S3.S33308

• Journal Article Type: Article
• Acceptance Date: Jul 26, 2024
• Online Publication Date: Aug 29, 2024
• Publication Date: Aug 29, 2024
• Deposit Date: Aug 3, 2024
• Publicly Available Date: Aug 3, 2024
• Journal: Journal of Biomedical Optics
• Print ISSN: 1083-3668
• Electronic ISSN: 1560-2281
• Publisher: Society of Photo-optical Instrumentation Engineers
• Peer Reviewed: Peer Reviewed
• Volume: 29
• Issue: S3
• Article Number: S33308
• DOI: https://doi.org/10.1117/1.JBO.29.S3.S33308
• Public URL: https://nottingham-repository.worktribe.com/output/37990024
• Publisher URL: https://www.spiedigitallibrary.org/journals/journal-of-biomedical-optics/volume-29/issue-S3/S33308/Exploring-the-bias--how-skin-color-influences-oxygen-saturation/10.1117/1.JBO.29.S3.S33308.full#_=_